Administrators NorthGeorgiaWX Posted December 23, 2023 Administrators Share Posted December 23, 2023 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0649 AM CST Sat Dec 23 2023 Valid 231300Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN HIGH PLAINS... ...SUMMARY... Isolated severe thunderstorms are possible across parts of the southern High Plains, mainly this afternoon and evening. ...Synopsis... In mid/upper levels, phasing of northern and southern streams over the western CONUS will result in a full-latitude trough by the end of the period, from east-central MT southward over the central/ southern Rockies to eastern Chihuahua. This will occur as a weakening cyclone -- now centered over southern/central AZ -- ejects northeastward to the central High Plains by 12Z tomorrow, and weakens considerably. Meanwhile, a northern-stream shortwave trough -- evident in moisture-channel imagery over the northern Rockies -- will split, with the southern part digging south-southeastward to NM, and the northern part evolving to a 500-mb low over east-central MT by 12Z tomorrow. Height falls associated with this process will spread across the Great Plains. As that occurs, a long, broad fetch of low-level warm advection and moisture-transport will strengthen, expand laterally, and shift eastward over the Plains States through the period. At the surface, a cold front now moving across the Canadian border into MT will cross the northern High Plains today, then continue eastward and southeastward. Meanwhile, lee troughing over the High Plains will deepen and be overtaken by the front from north-south. By 00Z, the front should extend from the central Dakotas across western NE to a low over central/east-central CO. A weaker cold front -- preceding the southern-stream perturbation -- will emerge from the southern Rockies, reaching near the lee-trough position over eastern NM and far west TX around 00Z. By 12Z, the cold front should extend from a weak low over northwestern MN, across eastern SD, southern NE, western KS, to northeastern NM. A broad wind-shift zone, representing the remnant southern front and lee trough -- should extend by then from the eastern TX Panhandle southward to eastern Coahuila. ...Southern High Plains... Scattered thunderstorms should develop late this afternoon into evening, and sweep eastward to northeastward across the outlook area. Damaging to locally severe gusts and isolated large hail are possible. Within the broad belt of currently sub-15% severe-type probabilities, wind appears to be a somewhat greater threat than hail, especially over eastern parts of the outlook, where a squall line should become the main convective mode. While a tornado cannot be ruled out, that threat appears very conditional. Activity should develop as the plume of large-scale ascent and low-level convergence (near the southern front and lee trough) increasingly overlap, and related lift impinges on a moistening, gradually destabilizing sector from the TX Panhandle across the Permian Basin and Big Bend regions. Diurnal/diabatic destabilization will be restricted by cloud cover, and in some areas, precip. Still, positive theta-e advection is expected throughout the day, underlying cooling temperatures aloft from mid-afternoon onward. Resulting weakened MLCINH and increased (but still modest) lapse rates will boost buoyancy, with 50s F surface dewpoints over most of the area and near 60 along the Rio Grande just upstream from DRT. This should support MLCAPE ranging from around 1000 J/kg in the Big Bend area to 300-500 J/kg over the southern Panhandle and South Plains regions. Low-level and deep shear will favor early-stage supercell potential, though pronounced weaknesses should be noted in hodographs between 1-3 km. Effective-shear magnitudes of 40-50 kt should become common in the immediate preconvective environment. Upscale development into a QLCS is likely before the activity outruns its supporting plume of favorable surface-based buoyancy, which will be narrow in east-west extent. While elevated thunderstorms may persist for some distance eastward, a combination of more-stable near-surface air and messier, more-linear convective mode will reduce the severe threat with eastward extent into northwest through west-central TX and western OK tonight. Still, slightly more room has been allotted on the eastern rim of the outlook for this transition to occur. ..Edwards/Broyles.. 12/23/2023 Read more View the full article Quote Link to comment Share on other sites More sharing options...
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